Ofdm transmitter apparatus and ofdm receiver apparatus

ABSTRACT

An OFDM transmitter apparatus and an OFDM receiver apparatus wherein the calculation amount of cell search can be reduced and a faster cell search and a reduced circuit scale can be accomplished. A base station apparatus ( 100 ), which serves as an OFDM transmitter apparatus, comprises an SCH inserting part ( 130 ) that serves as a frame forming means for forming a frame in which synchronous sequences are arranged such that symbols located symmetrically about a subcarrier of a DC component are complex conjugates; and an IFFT part ( 135 ) that servers as an OFDM modulation means for OFDM modulating the formed frame. Thus, at a mobile station apparatus ( 200 ), which receives the frame, only a real number signal can be used as an SCH replica signal to perform a correlation processing, so that the calculation amount can be reduced and a faster cell search can be accomplished.; In addition, because of the reduced calculation amount, the circuit scale at the receiving end can be reduced.

TECHNICAL FIELD

The present invention relates to an OFDM transmitting apparatus and anOFDM receiving apparatus. More particularly, the present inventionrelates to an OFDM transmitting apparatus transmitting synchronizedsequences and an OFDM receiving apparatus receiving the synchronizedsequences and performs synchronization control.

BACKGROUND ART

In the standards organization 3GPP (3rd Generation Partnership Project),studies are conducted for 3GPP LTE (Long Term Evolution) to realizefurther improvement of present third mobile phone systems. Thestandardization meeting in November, 2004, approves requirementconditions for LTE systems (see Non-Patent document 1), and the OFDMscheme is likely to be adopted as a downlink radio transmission schemeto meet these requirements.

In cellular systems such as mobile phone systems, cell search technique,which mobile stations search for the optimal base station to connect theradio link upon starting communication, upon handover, upon waitingcommunication for carrying out intermittent reception, and so on, is oneof significant functions. The standardization meeting proposes study ofcell search in LTE systems (see Non-Patent Document 2).

Non-Patent Document 2 discloses conducting cell search in the followingthree steps. In the first stage, correlation detection is performed withrespect to the first synchronized sequences (P-SCH: PrimarySynchronization Channel)in the time domain. This detects the OFDM symboltiming and subframe timing.

In the second stage, the correlation detection is performed with respectto the second synchronized sequences (S-SCH: Secondary SynchronizationChannel)in the frequency domain. This detects, for example, cell IDgroups, radio frame timings, cell structures, MIMO antenna structuresand BCH bandwidth.

In the third step, correlation detection is performed with respect tothe common pilot channels in the frequency domain. To be more specific,correlations between replicas of common pilot signals and receivedsignals after FFT are detected. This detects cell IDs belonging to cellID groups detected in the second step (that is, identifies cell-specificscramble codes) and identifies the sector numbers.

As described above, by detecting correlation between replica signals ofsynchronization channel (SCH) held in receiving apparatuses and receivedsignals, timings can be detected.

-   Non-patent Document 1: 3GPP, TR 25.913 v7.0.0(2005 June),    “Requirements for Evolved UTRA and UTRAN”-   Non-patent Document 2: 3GPP, R1-060780, NTT DoCoMo, NEC, “SCH    Structure and Cell Search Method for E-UTRA Downlink”

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

Incidentally, to start communication earlier, demanded is high speedcell search. Further, if the amount of calculation can be reduced torealize high speed cell search, it is possible to reduce circuit scaleand power consumption of communication apparatuses.

The present invention is made in view of the above-described problems,and it is therefore an object of the present invention to provide anOFDM transmitting apparatus and OFDM receiving apparatus that reducesthe amount of calculation of cell search and realizes high speed cellsearch and reduced circuit scales.

Means for Solving the Problem

The OFDM transmitting apparatus of the present invention adopts aconfiguration including: a synchronization sequence forming section thatforms a synchronized sequence with a real number alone or with animaginary number alone; and an OFDM signal forming section that forms anOFDM transmitting signal including the synchronized sequence.

The OFDM receiving apparatus of the present invention adopts aconfiguration including: a receiving section that receives an OFDMsignal including a synchronized sequence formed with a real number aloneor with an imaginary number alone; and a timing detecting section thatdetects correlation using a synchronized sequence replica formed withthe real number alone or with the imaginary number alone.

Advantageous Effect of the Invention

According to the present invention, it is possible to provide an OFDMtransmitting apparatus and OFDM receiving apparatus that reduces theamount of calculation of cell search and realizes high speed cell searchand reduced circuit scales.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of the base stationapparatus according to Embodiment 1 of the present invention;

FIG. 2 explains the SCH sequences the base station of FIG. 1 transmits;

FIG. 3 is a block diagram showing the configuration of the mobilestation apparatus according to Embodiment 1 of the present invention;

FIG. 4 explains the SCH sequences the base station in Embodiment 2transmits;

FIG. 5 is a block diagram showing the configuration of the base stationapparatus according to other embodiments; and

FIG. 6 is a block diagram showing the configuration of the mobilestation apparatus according to other embodiments.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings. In the embodiments, thesame reference numerals are assigned the same components, and thereforethe overlapping descriptions will be omitted.

Embodiment 1

The radio communication system in Embodiment 1 has a base stationapparatus and a mobile station apparatus. Referring to FIG. 1, basestation apparatus 100 of Embodiment 1 has error correction codingsection 105, modulating section 110, scrambling code generating section115, scrambling processing section 120, SCH generating section 125, SCHinserting section 130, IFFT section 135, CP inserting section 140, timewindowing (“TW”) processing section 145 and RF transmitting section 150.

Error correction coding section 105 performs predetermined coding ontransmission data, which is an input signal, and outputs the codedtransmission data to modulating section 110.

Modulating section 110 performs predetermined primary modulation on thesignal after coding processing, which is an input signal, and outputsthe modulated signal to scrambling processing section 120.

Scrambling code generating section 115 generates a scrambling codeaccording to the ID that is specific to the cell of the base stationapparatus, and outputs the scrambling code to scrambling processingsection 120.

Scrambling processing section 120 performs scrambling by multiplying themodulated signal, which is an input signal, by the scramble code, andoutputs the scrambled signal to SCH inserting section 130.

SCH generating section 125 generates an SCH sequence formed with pairsof symbols, which are complex conjugates of each other, and outputs theSCH sequence to SCH inserting section 130.

SCH inserting section 130 maps the SCH sequence generated in SCHgenerating section 125 to a frame in the frequency domain (i.e. to anOFDM symbol). To be more specific, SCH inserting section 130 maps theSCH sequence in a frame in the frequency domain so that subcarriersymbols in symmetric positions with respect to the subcarrier of the DCcomponent (hereinafter “DC subcarrier”) are complex conjugates of eachother. Now, this configuration in which subcarrier symbols in symmetricpositions with respect to the DC subcarrier are complex conjugates ofeach other will be hereinafter referred to as being “complex conjugatesymmetric” in the present description. In other OFDM symbols, the signalscrambled in scrambling processing section 120 is mapped.

IFFT section 135 performs an inverse fast Fourier transform of the inputsignal and converts the frequency domain signal into a time domainsignal, to generate an OFDM signal, and outputs the OFDM signal to CPinserting section 140. At this time, the SCH sequence inserted in SCHinserting section 130 is “complex conjugate symmetric,” so that, uponthe inverse fast Fourier transform in IFFT section 135, only the realnumber part of the SCH sequence remains and gives a real number signal.

CP inserting section 140 maps a copy of the tail part of the inputtedOFDM symbol to the beginning of that OFDM symbol, that is, inserts acyclic prefix (“CP”).

TW processing section 145 filters the OFDM signal for maintaining thecontinuity of the waveform of the OFDM signal after inserting a CP, andoutputs the OFDM signal after the filtering processing to RFtransmitting section 150.

RF transmitting section 150 performs radio processing (e.g. D/Aconversion and up-conversion) on the input signal and transmits theinput signal subject to radio processing via antenna.

Referring to FIG. 3, mobile station apparatus 200 of Embodiment 1 has RFreceiving section 205, SCH replica signal generating section 210, P-SCHcorrelation detecting section 215, FFT section 220, S-SCH correlationdetecting section 225, cell ID group detecting section 230, pilotcorrelation detecting section 235, scrambling code detecting section240, descrambling processing section 245, demodulating section 250 anderror correction decoding section 255.

RF receiving section 205 performs radio receiving processing (e.g. A/Dconversion and down-conversion) on a received signal received via theantenna, and outputs the received signal after radio receivingprocessing to P-SCH correlation detecting section 215 and FFT section220.

SCH replica signal generating section 210 generates an SCH replicasignal, which is a real number signal similar to the output of IFFTsection 135 of base station apparatus 100, and outputs the SCH replicasignal to P-SCH correlation detecting section 215.

P-SCH correlation detecting section 215 finds the correlation betweenthe SCH replica signal and the received signal and detects the timing apeak occurs (e.g. symbol timing, subframe timing, etc.), and outputstiming information to FFT section 220.

FFT section 220 removes the CP based on the timing information (i.e.symbol timing) inputted from P-SCH correlation detecting section 215.Further, FFT section 220 performs a fast Fourier transform at the timingbased on the timing information (i.e. symbol timing), and outputs thesignal after the fast Fourier transform to S-SCH correlation detectingsection 225, pilot correlation detecting section 235 and descramblingprocessing section 245.

S-SCH correlation detecting section 225 detects the correlation betweenthe signal after the FFT (i.e. the signal converted in the frequencydomain) and an SCH sequence, and output cell ID group detecting section230.

Based on the correlation result detected in S-SCH correlation detectingsection 225, cell ID group detecting section 230 detects the cell IDgroup and outputs the detected cell ID group information to scramblingcode detecting section 240.

Pilot correlation detecting section 235 detects the correlation betweenthe signal after the FFT and the pilot sequence, and outputs the signalafter correlation detecting to scrambling code detecting section 240. Tothe transmission frame transmitted from base station apparatus 100, apilot sequence, in which a cell specific scrambling code and the OFDMsymbol at the predetermined position from the beginning of the frame aremultiplied, is mapped. For the reason, the frame timing can be detectedby finding the correlation between the signal after FFT processing andthe pilot sequence.

Scrambling code detecting section 240 identifies the frame timing fromthe correlation detection result in pilot correlation detecting section235, specifies the position of the pilot sequence from this frametiming, and detects the peak by multiplying this pilot sequence by thescramble code included in the cell ID group that the cell ID groupinformation designates, thus identifying the scramble code. This fixedscramble code is outputted to descrambling processing section 245.

Descrambling processing section 245 descrambles the signal after FFTprocessing using the scramble code detected in scrambling code detectingsection 240, and outputs the signal to demodulating section 250.

Demodulating section 250 demodulates the input signal and outputs thedemodulated signal to error correction decoding section 255. Errorcorrection decoding section 255 performs predetermined decoding toacquire received data.

Next, the operations of base station apparatus 100 and mobile stationapparatus 200 having the above configurations will be explained.

In base station apparatus 100, SCH generating section 125 generates anSCH sequence formed with pairs of symbols, which are complex conjugatesof each other, and outputs the SCH sequence to SCH inserting section130.

SCH inserting section 130 maps the SCH sequence in a frame so thatsubcarrier symbols in symmetric positions with respect to the DCsubcarrier are complex conjugates of each other. That is, in SCHinserting section 130, a frame is formed in which an SCH sequence ismapped such that subcarrier symbols in symmetric positions with respectto the DC subcarrier are complex conjugates of each other.

IFFT section 135 performs an inverse fast Fourier transform of the framewhere the SCH sequences are mapped, such that subcarrier symbols insymmetric positions with respect to the DC subcarrier are complexconjugates of each other. As described above, in the OFDM signal afterIFFT, only the real number part of the SCH sequence remains.

The OFDM signal is subject to predetermined processing in CP insertingsection 140, TW processing section 145 and RF transmitting section 150,and transmitted via antenna.

In mobile station apparatus 200, RF receiving section performspredetermined processing on a received signal received via antenna, andoutputs the received signal to P-SCH correlation detecting section 215.

P-SCH correlation detecting section 215 finds correlation between theSCH replica signal and the received signal. Here, regarding receivedsignal, although the SCH sequence includes the real number signal alonewas transmitted from base station apparatus 100, phase rotation isproduced over the channel, and therefore, upon reception, the receivedsignal includes the imaginary number part as well such as(I_(RECEIVE)+j×Q_(RECEIVE)) However, the SCH sequence of the receivedsignal is influenced by phase rotation alone, so that P-SCH correlationdetecting section 215 can find correlation by using I_(REPLICA) as anSCH replica signal.

That is, for conventional correlation calculation, the followingequation is required to calculate.

(I _(RECEIVE) +j×Q _(RECEIVE))×(I _(REPLICA) +j×Q _(REPLICA))

where “*” is the complex conjugate.

By contrast with this, in the mobile station apparatus 200, it is enoughto calculate the following equation.

(I _(RECEIVE) +j×Q _(RECEIVE))×I _(REPLICA)

Consequently, the amount of calculation in mobile station apparatus 200may be about a half amount of the conventional correlation calculation,so that it is possible to reduce the circuit scales of correlationdetection.

In this way, according to the present embodiment, the base stationapparatus 100 as an OFDM transmitting apparatus has: SCH insertingsection 130 as a frame forming means for forming a frame wheresynchronized sequences are mapped such that subcarrier symbols insymmetric positions with respect to the DC subcarrier are complexconjugates of each other; and IFFT section 135 as an OFDM modulationmeans for OFDM modulating the frame.

By this means, in the receiving side of the frame, it is possible tofind correlation by using a real number signal (i_(replica)) of an SCHreplica signal, so that the amount of calculation can be reduced andcell search can be made high speed. Further, the amount of calculationdecreases, so that it is possible to reduce the circuit scale at thereceiving side.

Further, according to the present embodiment, mobile station apparatus200 as an OFDM receiving apparatus has: RF receiving section 205 as areceiving means for receiving a frame where synchronized sequences(P-SCHs) are mapped, such that subcarrier symbols in symmetric positionswith respect to the DC subcarrier are complex conjugates of each other;and P-SCH correlation detecting section 215 as a timing detection meansfor detecting correlation using a synchronization sequence replica of areal number signal similar to the result of the synchronized sequencesubject to OFDM modulation.

By this means, by receiving the frame where synchronized sequences(P-SCHs) are mapped such that subcarrier symbols in symmetric positionswith respect to the DC subcarrier are complex conjugates of each other,the synchronized sequences can be found correlation only by the realnumber signal, so that the amount of calculation can be reduced and cellsearch can be made high speed. Further, the amount of calculationdecreases, so that it is possible to reduce the circuit scale.

Embodiment 2

In Embodiment 1, a frame is formed in which SCH a sequence is mappedsuch that subcarrier symbols in symmetric positions with respect to theDC subcarrier are complex conjugates of each other, and, in thereceiving side of this frame, the real number signal alone of an SCHreplica signal is used and correlated with a received signal. Bycontrast with this, in Embodiment 2, the frame is formed where SCHsequences are mapped such that subcarrier symbols in symmetric positionswith respect to the DC subcarrier are complex conjugates of each otherand the symbols on one side are furthermore code-inverted to the symbolson the other side.

The configuration of the radio communication system of the presentembodiment is the same as in Embodiment 1, and will be explained usingFIGS. 1 and 3.

SCH inserting section 130 maps the SCH sequences in a situation wheresubcarrier symbols in symmetric positions with respect to the DCsubcarrier are complex conjugates of each other as shown in FIG. 4, andthe symbols on one side are furthermore code-inverted to the symbols onthe other side. That is, in SCH inserting section 130, the frame isformed where the SCH sequences are mapped such that subcarrier symbolsin symmetric positions with respect to the DC subcarrier are complexconjugates of each other and the symbols on one side are furthermorecode-inverted to the symbols on the other side.

For the reason, with Embodiment 2, in the OFDM signal after IFFT by IFFTsection 135, only the imaginary number part of the SCH sequence remains.

P-SCH correlation detecting section 215 of the receiving side findscorrelation between the SCH replica signal and the received signal.Here, regarding received signal, although the SCH sequence includes theimaginary number signal alone was transmitted from base stationapparatus 100, phase rotation is produced over the channel, andtherefore, upon reception, the received signal includes the imaginarynumber part as well such as (I_(RECEIVE)+j×Q_(RECEIVE)). However, theSCH sequence of the received signal is influenced by phase rotationalone, so that P-SCH correlation detecting section 215 can findcorrelation by using j×Q_(REPLICA)) * as an SCH replica signal.

That is, for conventional correlation calculation, the followingequation is required to calculate.

(I _(RECEIVE) +j×Q _(RECEIVE))×(I _(REPLICA) j×Q _(REPLICA))*

where “*” is the complex conjugate.

By contrast with this, in the mobile station apparatus 200, it is enoughto calculate the following equation.

(I _(RECEIVE) +j×Q _(RECEIVE))×(j×Q _(REPLICA))

Consequently, the amount of calculation in mobile station apparatus 200may be about a half amount of the conventional correlation calculation,so that it is possible to reduce the circuit scales of correlationdetection.

In this way, according to the present embodiment, the base stationapparatus 100 as an OFDM transmitting apparatus has: SCH insertingsection 130 as a frame forming means for forming a frame wheresynchronized sequences (P-SCHs) are mapped such that symbols insymmetric positions with respect to a direct current subcarrier arecomplex conjugates of each other and the symbols on one side arefurthermore code-inverted to the symbols on the other side; and IFFTsection 135 as an OFDM modulation means for OFDM modulating the frame.

By this means, in the receiving side of the frame, it is possible tofind correlation by using an imaginary number signal ((j×Q_(REPLICA))*)of an SCH replica signal, so that the amount of calculation can bereduced and cell search can be made high speed. Further, the amount ofcalculation decreases, so that it is possible to reduce the circuitscale at the receiving side.

Further, according to the present embodiment, mobile station apparatus200 as an OFDM receiving apparatus has; RF receiving section 205 as areceiving means for receiving a frame where synchronized sequences aremapped in a situation where symbols in symmetric positions with respectto a direct component subcarrier are complex conjugates of each otherand the symbols on one side are furthermore code-inverted to the symbolson the other side; and P-SCH correlation detecting section 215 as atiming detection means for detecting correlation using an imaginarynumber signal replica similar to the result of the synchronized sequencesubject to OFDM modulation.

By this means, mobile station apparatus 200 as an OFDM receivingapparatus receives a frame where synchronized sequences are mapped in asituation where symbols in symmetric positions with respect to a directcurrent subcarrier are complex conjugates of each other and the symbolson one side are furthermore code-inverted to the symbols on the otherside, so that the correlation of the synchronized sequence can be foundby the imaginary number signal alone, thereby reducing the amount ofcalculation and making high speed cell search. Further, the amount ofcalculation decreases, so that it is possible to reduce the circuitscale.

Other Embodiments

(1) When subcarriers are mapped, usual OFDM modulation may be performedwithout the mapping of Embodiment 1 or 2, and the real number componentor pure imaginary number component alone of the OFDM signal may betransmitted. At this time, only one of the real number component and thepure imaginary number component is transmitted, so that it is necessaryto double the transmission power to compensate for power loss. This alsoresults in the same signal as in Embodiments 1 and 2 (complex conjugatesymmetric mapping or complex conjugate symmetric and code-inversionmapping).

(2) A known signal sequence between the base station apparatus and themobile station apparatus is used for the SCH sequence, and so, it is notnecessary to perform OFDM modulating processing in Embodiments 1, 2 andother embodiment (1), and the SCH signal can be held in a memory andtransmitted or can be inputted to correlation detecting processing.FIGS. 5 and 6 show the configurations of the base station apparatus andthe mobile station apparatus in this case.

As shown in FIG. 5, base station apparatus 300 has SCH signal memorysection 310 and SCH inserting section 320.

SCH signal memory section 310 stores the real number signal of the SCHsequence after IFFT in Embodiment 1 and the imaginary number signal ofthe SCH sequence after IFFT in Embodiment 2.

SCH inserting section 320, which is different from SCH inserting section130 in Embodiment 1, is provided after IFFT section 135. SCH insertingsection 320 combines the signal after the IFFT and the SCH sequence fromSCH signal memory section 310, and outputs the combined signal to CPinserting section 140.

Referring to FIG. 6, mobile station apparatus 400 has SCH signal memorysection 410 and P-SCH correlation detecting section 420.

SCH signal memory section 410 stores the same signal as SCH signalmemory section 310 at the transmitting side.

P-SCH correlation detecting section 420 finds the correlation betweenthe SCH replica signal from SCH signal memory section 410 and a receivedsignal, and detects the symbol timing and subframe timing.

INDUSTRIAL APPLICABILITY

The OFDM transmitting apparatus and OFDM receiving apparatus of thepresent invention are suitable for use in reducing the amount ofcalculation of cell search, and in realizing high speed cell search andreduced circuit scales.

1. An orthogonal frequency division multiplexing transmitting apparatus comprising: a synchronization sequence forming section that forms a synchronized sequence with a real number alone or with an imaginary number alone; and an orthogonal frequency division multiplexing signal forming section that forms an orthogonal frequency division multiplexing transmitting signal including the synchronized sequence.
 2. An orthogonal frequency division multiplexing receiving apparatus comprising: a receiving section that receives an orthogonal frequency division multiplexing signal including a synchronized sequence formed with a real number alone or with an imaginary number alone; and a timing detecting section that detects correlation using a synchronized sequence replica formed with the real number alone or with the imaginary number alone.
 3. An orthogonal frequency division multiplexing transmitting apparatus comprising: a frame forming section that forms a frame in which a synchronized sequence is mapped such that symbols in symmetric positions with respect to a direct current component subcarrier are complex conjugates; and an orthogonal frequency division multiplexing modulating section that orthogonal frequency division multiplexing modulates the frame.
 4. An orthogonal frequency division multiplexing transmitting apparatus comprising: a frame constructing section that constructs a frame to which synchronized sequences are mapped in a situation in which symbols in symmetric positions with respect to a direct component subcarrier are complex conjugates of each other and the symbols on one side are furthermore code-inverted to the symbols on the other side; and an orthogonal frequency division multiplexing modulating section that orthogonal frequency division multiplexing modulates the frame.
 5. An orthogonal frequency division multiplexing receiving apparatus comprising: a receiving section that receives a frame in which a synchronized sequence is mapped such that symbols in symmetric positions with respect to a direct current component subcarrier are complex conjugates; and a timing detecting section that detects correlation using a synchronized sequence replica of a real number signal similar to a result of the synchronized sequence subject to orthogonal frequency division multiplexing modulation.
 6. An orthogonal frequency division multiplexing receiving apparatus comprising: a receiving section that receives a frame to which a synchronized sequence is mapped in a situation in which symbols in symmetric positions with respect to a direct component subcarrier are complex conjugates of each other and the symbols on one side are furthermore code-inverted to the symbols on the other side; and a timing detecting section that detects correlation using a synchronized sequence replica of an imaginary number signal similar to a result of the synchronized sequence subject to orthogonal frequency division multiplexing modulation. 